When hip endoprostheses are being inserted, the surgeon must proceed through various stages of the operation in which tools are employed; in particular, it is necessary to use a bone cutter in order to mill out the natural acetabulum and thus form a bearing socket within which an artificial cup can be anchored. An impact instrument is also used to drive the cup into place. When using either tool the surgeon must take care that the tools are oriented as precisely as possible, so that the prosthesis cup will ultimately be positioned as intended, with the greatest possible precision.
Important accessories that assist correct positioning and orientation of the tools include so-called navigation systems that function with computer assistance. Obviously, such systems are quite elaborate, and the costs of employing them are correspondingly high. In view of the fact that in medicine, as elsewhere, it is important to reduce costs without any deterioration in the quality of medical care, the present invention is directed toward the objective of providing an accessory for the implantation of a hip joint endoprosthesis that allows exact positioning of the prosthesis cup in relation to the femur, specifically to the joint head anchored in the femur, with simple mechanical means. During this operation care must be taken to implant the cup in such a way that during every conceivable movement of the femur, a collision between the edge of the cup and the neck of the femur is avoided.